Posted
by
timothy
on Sunday April 17, 2011 @12:59PM
from the needs-an-instructables-page dept.

autospa writes with an intriguing story found at Nature about direct electrical stimulation's effect on the brain. By applying low levels of electrical current to different parts of the brain via electrodes placed on the scalp, University of New Mexico researchers claim to have documented some significant changes in brain activity, which vary depending on the part of the brain targeted. Gamers, take note: in one experiment in which volunteers were recorded while playing a video war game, "those receiving 2 milliamps to the scalp (about one-five-hundredth the amount drawn by a 100-watt light bulb) showed twice as much improvement in the game after a short amount of training as those receiving one-twentieth the amount of current." The idea of affecting the brain by electric stimulation isn't new; but the battery-powered, non-invasive variety naturally leads some people to consider rolling their own.

Very little is known about how TDCS works. Scientists theorize that the mild current primes the neurons for action but does not trigger the voltage spikes that neurons use to communicate. "Presumably, it is polarizing neurons and making them more or less likely to respond to inputs," says Warren Grill, a neural engineer at Duke University, in Durham, NC. "But what's happening at the level of the synapse, where the business of learning really takes place, we don't know."

Of course, given the opening sentence to that paragraph, it's probably not something you'd want to play with at home...

I'd hope that the people of slashdot would not be dumb enough to try this. You can KILL yourself with 9 VOLT BATTERY if you go through the skin. I would suggest that the editor note this in the summary. Telling, or even hinting at a crowd, especially tinkerers, to attempt such a thing is negligence. Sorry bloggers, but a "I'm not responsible" tag somewhere on the site doesn't actually make you not responsible, otherwise BP would have done that on all their rigs.

I took electrical engineering so I may have a touch of knowledge upon the subject.

A 9V battery is <40V and no one mentioned actually piercing the skin or actually removing your skin (what?) so I really don't think a 9V battery is a danger here.

Also, how are you going to ensure all the current from 2 electrodes placed ANYWHERE on the outside of the body go through your heart?

Anyways, if we were talking about higher voltages I might agree, but anyone touching themselves with a 9V battery ANYWHERE is probably a safe thing to do. Hell putting one on your tongue does not even generate enough current to make the muscle go into any kind of serious contraction, and that is about as close and low resistance as you can get.

Again, if you don't step the voltage up, or start driving nails into your skull/chest cavity and hook batteries up to them, i posit that 9V batteries can generally be considered safe, even to the uninformed.

Current is what will kill you, not voltage. Greater current causes greater voltage gradients inside of you, which will disrupt neurons more and increase power dissipation, burning things. Higher voltage is more dangerous because it increases current. Decreasing resistance also increases the current. Your skin is a pretty good insulator, but if you poke wires in deep enough that they reach the wet bits that protection is lost and the current will spike way up.

Here are some measurements on myself:2.5M ohm Probes pinched in my fingers of left and right hands500K ohm After licking fingertips1M ohm Across my scalp50K ohm Across my tongue

A 9V battery isn't going to come anywhere near 2mA with any of those contacts. For anyone who wants to try wiring up their brain, though, I suggest putting a 4.7K resistor in series with the 9V battery - the added resistance is insignificant next to your skin, but when you accidentally stab the electrodes straight through your skull and into your brain it'll limit the current to safe levels.

I also suggest that a 9V battery is worthless because of the resistance of your skin. If you want this to actually work you should use a much higher voltage (such as stepping that 9V up with an oscillator driving a transformer) and a much larger value of protection resistor (Ohm's Law [wikipedia.org]), to better approximate a constant-current source. A constant-current power supply is even better. Note that above 300V you're running a risk of dielectric breakdown [wikipedia.org] in your skin - IE, the resistance suddenly drops - and the current will surge. You'd better have a protection resistor that can save you from the highest possible open circuit voltage of whatever power supply you use.

Start low and work your way up. 1mA is enough to put you in v-fib [wikipedia.org] if it's direct to the heart. Of course, anything applied to the skin will spread out considerably before it reaches your heart - it's more like 50mA to the skin directly across the chest to induce v-fib - but it's best to have a healthy respect for what you're doing.